netdev - Re: [PATCH 4/5] virtio_net: enable premapped mode for merge and small by default

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Message-ID: <CACGkMEvPn2QUOdxhCk=efiGj+wT2yGv4wmUGpbXH-QGGToNMLw@mail.gmail.com>
Date: Fri, 18 Oct 2024 16:00:07 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>, 
	Eugenio Pérez <eperezma@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, virtualization@...ts.linux.dev
Subject: Re: [PATCH 4/5] virtio_net: enable premapped mode for merge and small
 by default

On Mon, Oct 14, 2024 at 11:12 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> Currently, the virtio core will perform a dma operation for each
> buffer. Although, the same page may be operated multiple times.
>
> In premapped mod, we can perform only one dma operation for the pages of
> the alloc frag. This is beneficial for the iommu device.
>
> kernel command line: intel_iommu=on iommu.passthrough=0
>
>        |  strict=0  | strict=1
> Before |  775496pps | 428614pps
> After  | 1109316pps | 742853pps
>
> In the 6.11, we disabled this feature because a regress [1].
>
> Now, we fix the problem and re-enable it.
>
> [1]: http://lore.kernel.org/all/8b20cc28-45a9-4643-8e87-ba164a540c0a@oracle.com
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>  drivers/net/virtio_net.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index cd90e77881df..8cf24b7b58bd 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -6133,6 +6133,21 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
>         return -ENOMEM;
>  }
>
> +static void virtnet_rq_set_premapped(struct virtnet_info *vi)
> +{
> +       int i;
> +
> +       /* disable for big mode */
> +       if (vi->mode == VIRTNET_MODE_BIG)
> +               return;

Nitpick: I would like such a check to be done at the caller.

But anyhow the patch looks good

Acked-by: Jason Wang <jasowang@...hat.com>

Thanks

> +
> +       for (i = 0; i < vi->max_queue_pairs; i++) {
> +               /* error should never happen */
> +               BUG_ON(virtqueue_set_dma_premapped(vi->rq[i].vq));
> +               vi->rq[i].do_dma = true;
> +       }
> +}
> +
>  static int init_vqs(struct virtnet_info *vi)
>  {
>         int ret;
> @@ -6146,6 +6161,8 @@ static int init_vqs(struct virtnet_info *vi)
>         if (ret)
>                 goto err_free;
>
> +       virtnet_rq_set_premapped(vi);
> +
>         cpus_read_lock();
>         virtnet_set_affinity(vi);
>         cpus_read_unlock();
> --
> 2.32.0.3.g01195cf9f
>